Signal generator



Nov. 22, 1955 e. w. SHERWIN SIGNAL GENERATOR Original Filed Jan. 4, 1945 WIDE GATE GENERATOR INVENTOR GHALMERS W. SHERWIN A TTORNEY sine wave signals that have a aluniform initial amplitude.

2,724 ,7 7 6 t to SIGNAL GENERATOR Chalmers W. Sherwin, Champaign, Ill., assignor, by mesne assignments, to the United States of America. as represented by the Secretary of the Navy Original application January 4 1945 Serial No. 571 31s. Divided and this application; September 27, 19511 SerialNo.248,595 t t 7 Claims. (Cl. 25036) 1 necessary or desirable to generate a train of oscillations of substantially constant amplitude and of sinusoidal forjrn. In certain of these instances it is desired that the oscillations start in a fixed phase relationship with a second signal, continue at a substantially fixed amplitude for a preselected interval of time and then abruptly cease. i H j Heretofore such interrupted trains of sinusoidal oscillationshave been generated by shock exciting a normally passive, capacitor-inductor tuned circuit with a serieslof spaced pulses. Usually these pulses arecoupled to the tuned circuit through an electron tube amplifier normally biased far beyond cutoff. The spacing between pulses is .usuallymade equal to the spacing between the initial cycles of successive wave trains and the duration of these p ulses is usually much less than the duration of a half cycle of the desired oscillation. t Signal generators of this type are subject to several disadvantages; the shape of the initial cycle and the phase and amplitude of the initial oscillations may vary considerably with only a minor change in characteristic of the initiating pulse. If the waveftrain is to continue for a large fraction of the interval between successive, wave trains, it is necessary to provide additional damping circuits toterminate the oscillation after the desired interval or to so highly damp the tuned circuit that the decrement ofthe"oscillationbecomes objectionable. Ifthe oscillations are allowed to continue from one wave train to the next, some unstability of operation may result from. the

phase with the oscillations already present in the tuned circuit. t t

Therefore, it is an object of the present invention to provide a signalgenerator which overcomes all of the disadvantages outlined above. y v

A more specific object of the present invention is to provide a signal generator that will generate interrupted precise starting phase and ;A further object of the present invention is to provide 1 a, signal generator for producing oscillations that continue at a uniform amplitude for a selected timeinterval and then abruptly cease.

In general, the above objects are accomplished by providing a signal generator circuit in whicha capacitorinductor tuned circuitis normally flooded with current from a low impedance source and in which said current is interrupted for a preselected interval to allow said tuned circuit to oscillate.

Qther objects, features and advantages of the present fact that the'initiating pulses may not occur in proper 2,724,776 Patented Nov. 2 2 1 invention will become apparent from the following specification which is to be read in conjlunction with the accompanying drawing in which:

Fig. 1 is a schematic diagram of a ment of the present invention; and t Fig. 2 is a series of voltage time plots which illustrate the operation of the circuit shown in Fig. 1. t

Referring now to Fig. 1, 10 is a wide gate generator which produces a negative gate of a duration equal to the desired duration of the wave train to be generated. Wide gate generator 10 may take the form of a unistable multivibrator which is caused to generate the negative gate by the application of a relatively narrow pulse at terminals 12. Alternatively, wide gate generator may be a free-running. circuit having a natural period slightly longer than the interval between the pulses at terminals 12. The output of generator 10 is coupled to the conventional resistor-capacitor grid circuit of an electron tube 16. Terminal 18 of coupling network 14 is returned to a source of positive bias to assure that tube 16 remains normally conducting. The anode of tube 16 is connected to the positive terminal 20 of an anode potential source schematically represented by the plus sign through a con ventional resistor-capacitor voltage dropping decoupling network 22. Network 22 may be omitted and the anode of tube 16 may be returned directly to the terminal 20 if the anode potential source is of the proper potential. The cathode of tube 16 is connected to arm 24 of a switch having three contacts 26,28 and 30. It is to be understood that the number of contacts on the switch may be varied without departing from the scopeof the present invention. Contacts 26, 28 and 30 are connected to the negative terminal of the anode potential source, here represented as being at ground potential, through preferred embodi parallel inductance-capacitorcircuits 32, 34 and 36, re-

spectively. The natural resonant frequencies of circuits 32, 34 and36 are equal to thedesired frequencies of the: sinusoidal signals to be generated. The cathode of tube 16 is also connected through a resistor 38 to the grid of an electron tube amplifier stage represented in Fig. 1 by the mode tube 40.

The circuit illustrated in Fig. 1 operates in the follow ing manner. Thewaveformshown in Fig. 2A is applied to terminals 12 as illustrated by the letter A in Fig. 1. The spacing between the pulses 42 in Fig. 2A is made,

equal to the desired interval between successive wave 2B. The negative portions by the circuit constants of generatorlO. t The duration of negative portion 44 is selected to be equal to the desired duration of'thewave trains and the.

amplitudeis suflicient to overcomethe bias on tube 16 and cause anode current cutoif in this tube. 3' With arm 24 connected to contact 26 the inductor in circuit 32 is normally flooded with current. Upon the apthe normal source or is cut ofl. However, the potential at the cathode of tube 16 does not drop voltage in the inductor. This induced voltage causes circulating currents to flow in circuit 32 charging the capacitor in circuit 32. It"

can be shown that the voltage across the inductor will plication of a negative gate to tube 16 supply of this current through tube 16 abruptly because of the self-induced continue to follow a sinusoidal curve as the energy stored in circuit 32 is continually exchanged between the capacitor and the inductor. If the coupling circuit through resistor 38 to amplifier 40 is made such that there is no appreciable damping of circuit 32, the oscillations will remain at substantially constant amplitude for several cycles.

At the termination of the negative portion of the signal applied to the grid of tube 16 anode current again flows through tube 16 flooding circuit 32 and rapidly damping out the oscillations therein. Fig. 2C illustrates the signal at the cathode of tube .16.

It" should be noted that the wave train 46 of Fig. 2C always starts off with a full negative half cycle at the leading edge of the negative portion 44 of Fig. 2B. The exact shape of the negative portion 44 is of little importance since its only function is to maintain tube 16 cut off during the generation of wave train 46.

, Moving arm 24 to contact '28 or 30 will change the period of each cycle of the wave train 46 but will not otherwise alter the operation of the invention.

- One obvious modification of the circuit of Fig. 1 would be-to replace electron tube 16 with a difierent type of electronic switch. For example, a diode having its anode connected .to the output of generator through a suitable biasing network and its cathode connected to arm 24 would cause the circuit to operate in substantially the same manner.

It will be understood that while the description has been directed to what is at present considered to be the prefer-red embodiment of the present invention the actual scope of the invention includes all such modifications as are suggested by the above description and which fall within the limits defined by the following claims.

What is claimed is:

1. A circuit for producing a discontinuous train of oscillations, comprising'a source of potential having positive and negative terminals, an electron tube having at least an anode, a cathode and a control grid, said anode being coupled to said positive terminal, an inductor-capacitor tuned circuit interposed between the cathode of said tube and said negative terminal, means biasing said grid to a potential sufficient to cause said tube to pass current, and means coupled to said grid for interrupting said current for the interval in which said train of oscillations is to be generated whereby said tuned circuit is shock-excited into oscillation during said interval and whereby at the termination of said interval the flow of current through said tuned circuit quenchcs said oscillation.

2. A circuit for producing a discontinuous train of oscillations, comprising a source of potential having positive and negative terminals, an electron tube having at least an anode, a cathode and a control grid, said anode being coupled to said positive terminal, a plurality of inductor-capacitor tuned circuits each having one terminal thereof connected to said negative terminal, switch means for selectively connecting one of said tuned circuits to said cathode through a second terminal on said tuned circuit, means biasing said grid to a potential sufficient to cause said tube to pass current and means coupled to said grid for interrupting said current for the interval in which said train of oscillations is to be generated whereby said tuned circuit is ,shock excited into oscillation during said interval and whereby at the termination of said interval the flow of current through said tuned circuit quenchcs said oscillation.

3. A circuit for producing a discontinuous train of oscillations in. response to a series of time spaced pulses comprising a',source of potential having a positive and negative terminal, an electron tube having at least an anode, a cathode and a control grid, said anode being coupled to said positive terminal, a plurality of inductorcapacitor tuned circuits each having one terminal thereof connected to said negative terminal, switch means for selectively connecting one of said tuned circuits to saidcathode through a second terminal on said tuned circuit, means biasing said grid to a potential sutlicient to cause said tube to pass current, a negative gate generator responsive to said time spaced pulses, said generator being coupled to said grid to cause anode current cutofi' in said tube for the duration of the negative gate generated thereby, whereby said tuned circuit is shock excited into oscillation by the cutoff of anode current and whereby said oscillations are quenched by the resumption of anode current flow.

4. Apparatus for producing a discontinuous oscillations, comprising a vacuum tube having atleast an anode and a cathode, an inductor-capacitor'tuned circuit interposed between the cathode of said tube and ground, means for normally biasing said tube to pass current, and means for blocking said tube to current flow therethrough whereby to shock excite said tuned circuit into oscillation and for unblocking said tube after a predetermined interval of time to restore current flow therethrough and to thereby quench the oscillations in said tuned circuit.

5. A circuit for producing interrupted sine wave signals having a substantially uniform amplitude comprising, a source of current, an inductance-capacitance tuned circuit, switch means connecting said source of current to said tuned circuit and normally operative to supply current to said tuned circuit, and means for rendering said switch means inoperative to pass current at predetermined intervals, said interruption of current through said switch means acting to shock excite said tuned 'ci'r-,

cuit into oscillation.

6. A circuit for producing a discontinuous train of oscillations comprising, an inductorecapacitor tuned, circuit, a source of current coupled to said tuned circuit and normally supplying current to said tuned circuit,

and means associated with said current source and said tuned circuit adapted to periodically interrupt for a predetermined interval of time the flow of current to.

said tuned circuit whereby said'tuned circuit oscillates during said interval of interrupted current flow, said oscillations being rapidly quenched upon resumption cit current flow from said current source through said tuned circuit.

7.'A circuit for producing a discontinuous of oscillations in response to a series of time spaced pulses comprising, a vacuum tube having at least an anode, a cathode and a control grid, an inductor-capacitor tuned.

circuit interposed between the cathode of .said tube and ground, means for normally biasing said tube ,topass current, a negative gate generator responsive to. said' time spaced pulses, said generator being coupled to said,

grid to cause anode current cut-off in said tube for the duration of said negative gate, whereby said tuned circuit is shock excited into oscillation by the cut-off of anode current and whereby said oscillations are quenched by the resumption of anode current flow.

References Cited in the file of this .patent- I UNITED STATES PATENTS train of 

